长江口南槽中段枯季水沙输运特征研究

WATER AND SUSPENDED SEDIMENT TRANSPORTS IN THE MIDDLE REACH OF THE SOUTH PASSAGE IN THE CHANGJIANG ESTUARY DURING THE DRY SEASON

根据2015年1月7日至14日在长江口南槽中段主槽内获得的流速和悬沙观测资料,运用机制分解法分析了从大潮到小潮连续变化过程中南槽中段的水沙输运机制,通过小波分析方法探讨了悬沙浓度和流速的周期性对悬沙输运的影响。研究结果表明:(1)在一个大小潮周期过程中各潮周期的单宽净输水以向海为主,斯托克斯余流和欧拉余流的强度由大潮到小潮呈减小趋势;(2)各潮周期的单宽净输沙以向陆为主,与净输水方向相反,输沙强度从大潮至小潮呈现"小-大-小"的变化特征,该特征的产生与潮泵效应输沙的剧烈潮周期变化有关,平流输沙、潮泵效应输沙与垂向净环流输沙项是影响潮周期净输沙的主要成分;(3)小波分析表明,悬沙浓度和流速具有多个时间周期的变化,它们与水位的联合作用导致瞬时输沙率具有2个明显的时间周期变化。

Based on the data of current velocity and suspended sediment concentration measured in the main channel of the South Passage the Changjiang estuary from January 7 to 14 in 2015, the mechanisms of water and suspended sediment transports during a neap-spring tide cycle are analyzed by using the mechanism decomposition method. Furthermore, the influence of the periodic variation of suspended sediment concentration and current velocity on the suspended sediment transport is also explored by the method of wavelet analysis. The results showed that （1） the net water transport in most tidal cycles was seaward at the measurement station, and the magnitudes of the Euler and Stokes residual current decreased gradually from the spring tide to the neap tide. （2） The net suspended sediment transport was landward in each tidal cycle; from spring tide to neap tide the magnitude of suspended sediment transport displayed a remarkable ＂small - big - small＂ variation pattern owing to the intensively tidal variation of the tidal pumping transport; advection and net vertical circulation transport terms also play an important role on the net sediment transport. （3） The results of the wavelet analysis showed that the temporal variations of suspended sediment concentration and current velocity displayed several variation periods; the combined effect of suspended sediment concentration, flow velocity and water level leaded to 2 obvious variation period in the instantaneous sediment transport rate.